In computer graphics systems, users often wish to exclude portions of an image presented to them on a display screen. This operation is called “cropping”. To perform a cropping operation or crop, a user typically selects two points to define a rectangle (e.g. top left and bottom right corners) enclosing a selected portion of the original image. The portion of the original image outside of the rectangle is then excluded or cropped and an image of the selected portion alone, that is, a cropped image, is presented to the user.
One problem with present cropping methods is that a user may have difficulty selecting a desirable cropped image. Thus, a user may have to repeat the cropping operation several times in order to achieve the desired result.
One solution to this problem is suggested by Kasson in U.S. Pat. No. 5,473,740. Kasson describes a cropping method in which the cropped or excluded area of the image is blanked-out during the process of adjusting the rectangle defining the selected area. According to Kasson, the excluded portion of the image distracts the user and makes it more difficult to visualize the cropped image. In Kasson, a user moves a mouse to position a cursor on the original image and depresses the mouse pushbutton to designate a first corner (x1, y1) of the initially desired rectangular cropped image. The mouse is then manually moved and the sequentially updated position of the cursor instantaneously defines a second corner (x2, y2) diagonally opposite the first corner. While the mouse is moved and its pushbutton still depressed a sequentially varying area potential cropped image and a correspondingly sized obscured portion are displayed. If the user is satisfied with the aesthetics of the current cropped image, the user releases the mouse pushbutton, moves the cursor within the boundaries of the current cropped image and double clicks in order to select this cropped image for further processing, such as inclusion into a document being concurrently displayed in another window. Alternatively, any two of x1, y1, x2 and y2 can be updated by positioning the cursor over one of the four corners of the rectangular boundary of the current cropped image, depressing the mouse pushbutton, and holding it down while the cursor is moved.
Another solution was suggested by Cariffe, et al., in U.S. Pat. No. 6,201,548. Cariffe, et al. describe a cropping method in which after the cropped image has been formed and is displayed in a new window, the window containing the original image is also maintained and may be viewed concurrently with the cropped image. Moreover, the window containing the original image is preferably automatically minimized, that is, reduced in size to what is called an “iconified” version of the original, but may subsequently be restored to full size. If subsequent comparison by the user of both the original and cropped images side-by-side show an unwanted result, the cropping operation may then be repeated on the image in the original image window, which preferably does not get modified in any way by single or multiple sequential cropping operations.
However, while Kasson and Cariffer, et al. describe cropping methods that may provide a user with a desired cropped image after several iterations, neither of these methods provides for the accurate positioning of the bounds of the cropped image at the outset. Thus, and especially for large image presentations such as digital maps, a user may still have to repeat the cropping operation several times in order to accurately crop the original image. For example, while a user may use “panning” and “zooming” tools to view one corner of the rectangle defining the selected portion of an original image in order to relocate that corner, in doing so, the relative location of the second corner of the rectangle may be lost to the user or the user may find it difficult to determine what portion of the original image is being observed. In other words, while the user may have gained a detailed view of a region of the original image that is of interest, the user may lose sight of the context within which that region is positioned. This is an example of what is often referred to as the “screen real estate problem”.
Described herein are techniques that may provide for accurate digital image cropping. In addition, these techniques may be used to accurately select points in digital images for editing operations such as cropping and for related operations such as distance measurement.